This document describes EPA's decision to revise the national ambient air quality standards (NAAQS) for ozone (O<INF>3</INF>) based on its review of the available scientific evidence linking exposures to ambient O<INF>3</INF> to adverse health and welfare effects at levels allowed by the current O<INF>3</INF> standards. The current 1-hour primary standard is replaced by an 8-hour standard at a level of 0.08 parts per million (ppm) with a form based on the 3-year average of the annual fourth-highest daily maximum 8-hour average O<INF>3</INF> concentrations measured at each monitor within an area. The new primary standard will provide increased protection to the public, especially children and other at-risk populations, against a wide range of O<INF>3</INF>-induced health effects, including decreased lung function, primarily in children active outdoors; increased respiratory symptoms, particularly in highly sensitive individuals; hospital admissions and emergency room visits for respiratory causes, among children and adults with pre-existing respiratory disease such as asthma; inflammation of the lung, and possible long-term damage to the lungs. The current 1-hour secondary standard is replaced by an 8-hour standard identical to the new primary standard. The new secondary standard will provide increased protection to the public welfare against O<INF>3</INF>-induced effects on vegetation, such as agricultural crop loss, damage to forests and ecosystems, and visible foliar injury to sensitive species. EFFECTIVE DATE: This rule is effective September 16, 1997. ADDRESSES: A docket containing information relating to the EPA's review of the O<INF>3</INF> primary and secondary standards (Docket No. A-95- 58) is available for public inspection in the Central Docket Section of the U.S. Environmental Protection Agency, South Conference Center, Room 4, 401 M St., SW., Washington, DC. This docket incorporates the docket from the previous review of the O<INF>3</INF> standards (Doc